The present disclosure relates generally to a foil bearing with a trailing edge key, and more specifically, to a thin foil, hydrodynamic gas bearing comprising a trailing edge key to eliminate a foil fatigue failure.
In general, thin foil, hydrostatic journal bearings are used to support a rotating element in rotating machinery such as air cycle machines. Historically, the predominant journal loading was assumed to be static, (due to gravity or acceleration) or synchronous (1 time per shaft rotation); however, recent experience has shown that there are environments that impose a non-synchronous, high-cycle load on the thin foil, hydrostatic journal bearings. The journal bearing is comprised of several elements: top and intermediate foils are formed from a single-piece, double wrap cylindrical foil supported by a corrugated bump foil. When subjected to high levels of nonsynchronous loading, the formed key (anti-rotation) integral to the top/intermediate foil cracks (and in some cases separates). The crack initiates at a tight radius at a bottom of the formed key. The cracking is in part due to the geometry of the tight radius, which is an inherently high stress riser. Further, a forming operation necessary to fold the foil into a 180° bend exceeds an ultimate elongation of the foil itself, which leads to an orange peel condition and a degradation in the material fatigue strength.